Firstly, background art concerning the material for forming the protective film used in the dry exposure process will be discussed.
It has been conventionally known that a problem referred to as a stationary wave effect due to multiple interference occurs when a pattern is formed by exposing a photoresist film. That is, a phenomenon that an exposure light is transmitted through the photoresist film, and the transmitted light is reflected on an underlayer surface and a part of the reflected light is reflected on an upper surface of the photoresist film, the reflection being further repeated in the photoresist film.
The multiple interference by the light is attributed to interference of an irradiated light at a single wavelength, which has entered the photoresist film formed on the substrate, with the reflected light from the substrate, and light energy amounts absorbed in a thickness direction of the photoresist film are different. Variation in film thickness of the photoresist film affects a size width of the resist pattern obtained after development, resulting in reducing the accuracy of the size of the photoresist pattern.
This reduction in accuracy becomes a large problem because the film thickness of the photoresist film is different in concavoconvex portions, particularly when a fine pattern is formed on a substrate having different heights. Thus, it has been desired to develop technology in which the above interference effect is eliminated and the accuracy of the size of the resist pattern is not reduced even in a fine pattern formed on a substrate having different heights.
Consequently, a method in which a resin composition containing a material having a property of absorbing exposed light, applied on a semiconductor substrate to form an underlayer film (anti-reflection film) before forming a photoresist film on the substrate and the photoresist film is formed on the underlayer film (see Patent Document 1); and a method in which a water-soluble resin film of polysiloxane or polyvinyl alcohol as an anti-reflection film is formed on a photoresist film provided on a substrate (see Patent Documents 2 and 3) have been employed conventionally.
Next, background art concerning the material for forming the protective film used in the liquid immersion exposure process will be discussed.
In recent years, the liquid immersion exposure process has been reported as a new lithographic technique (see Non-patent Documents 1 to 3). In this liquid immersion exposure process, a conventional exposure light path space is replaced with a so-called liquid for liquid immersion exposure (e.g., pure water and a fluorine-based inert liquid and the like). Thereby, it is possible to realize the formation of a photoresist pattern having a higher resolution and an excellent focal depth even using a light source having the same exposure wavelength (see Patent Documents 4 to 6).
Technology which aims at simultaneously preventing alteration of the photoresist film due to the liquid for the liquid immersion exposure and variation in refractive index by using the protective film using a resin capable of being dissolved in only a particular solvent has been proposed (see Patent Document 5).
More recently, technology in which removing the protective film and forming the photoresist pattern are simultaneously performed upon alkali development after the liquid immersion exposure by using an alkali-soluble protective film has been proposed in terms of simplifying a resist pattern formation process and enhancing production efficiency (see Patent Document 6).    Non-Patent Document 1: Journal of Vacuum Science & Technology B (Published in U.S.A.), vol. 17, No. 6, pp. 3306-3309, 1999.    Non-Patent Document 2: Journal of Vacuum Science & Technology B (Published in U.S.A.), vol. 19, No. 6, pp. 2353-2356, 2001.    Non-Patent Document 3: Proceedings of SPIE (Published in U.S.A.), Vol. 4691, pp. 459-465, 2002.    Patent Document 1: U.S. Pat. No. 4,910,122    Patent Document 2: Japanese Patent Application, Publication No. H4-55323    Patent Document 3: Japanese Unexamined Patent Application, Publication No. H3-222409    Patent Document 4: PCT International Publication No. WO 2004/068242    Patent Document 5: PCT International Publication No. WO 2004/074937    Patent Document 5: Japanese Unexamined Patent Application, Publication No. 2005-264131